Field of the Invention
The present invention relates to integrated circuit technology. More particularly, the present invention relates to identifying that an integrated circuit has been manufactured using particular tooling.
Description of Related Art
Individual instances of the tooling used to produce integrated circuits results in nano- or atomic-scale differences in the manufactured integrated circuits (ICs) caused by uncontrollable differences introduced during the manufacturing of the tooling, when compared to integrated circuits manufactured using otherwise identical tooling produced from the same data. These differences are intentionally minimized to a point where they have no detrimental effect on the use of the tooling for its main intended purpose, i.e., to produce functional integrated circuits. Each copy of the tooling, even though not perfectly identical due to the inevitable uncontrolled unique variations from tool to tool, can all produce functional, nearly identical ICs.
Modern integrated circuits are produced with the aid of a photographic tool called a reticle, which includes geometric designs used to perform one process step, for example, to pattern a single implant or metal layer, for a single die or a small number of dice. The reticle is stepped across an entire wafer to pattern all the dice on the wafer. Even though the reticle may be thought of as one tool, if it includes nominally “identical” designs for patterning more than one IC at a time (as is usually the case unless the IC is exceptionally large where only one fits on the reticle), for the purposes of this invention, each of the copies of the design, even within a single reticle, will be considered as a particular instance of the tool. Some integrated circuit manufacturers keep records identifying the position on the wafer of the individual semiconductor die, and from this data and the stepping algorithm that was used, the specific instance of the tool used to produce a die is known.
In the prior art, watermarks can be intentionally introduced into tooling so that the individual ICs produced by each set of tooling can be readily identified by someone knowing the watermark. However, if a watermark can be intentionally introduced by the legitimate IC manufacturer, then it can also be cloned by an adversary.
Another prior art technique that can be used in this manner is known as physically unclonable function (PUF) technology. A PUF identifies the unique characteristics of each device, not the nearly invisible common characteristics imparted by the tooling. From a PUF point-of-view, this tooling-related correlation from device-to-device is undesirable as it reduces slightly the entropy exhibited by each device. In practice, the tooling-related correlation is so low that it does not materially affect PUF performance.
The need to ensure that an IC is from a trusted source, and is not a cloned device produced by an adversary, remains a vexing problem for both military and commercial applications. As production moves to ever more expensive facilities, which may not necessarily function under the desired security procedures demanded by the ultimate customer, this need becomes acute. What is needed, and not provided by the prior art, is a method to confirm that a received IC, or batch of ICs, are actually manufactured from trusted tooling, despite the manufacturing facility for the ICs not meeting the required security procedures.